This invention relates to a method and apparatus for the control of an internal combustion engine. While the general principles and teachings hereinafter disclosed are applicable to all combustion engines, the invention is hereinafter described in detail in connection with its application to a fuel-injected, spark-ignition internal combustion engine.
In the art of internal combustion engines, it is common practice to control the amount of fuel delivered to the engine in direct proportion to the rate of air flow introduced into the induction passage while controlling the ignition timing of the engine as a function of engine speed and induction passage air flow rate during normal engine operation and as a function of engine speed during engine idle operation.
With such a conventional engine control, several difficulties arise when a stepped change occurs in engine speed at idle or cruise conditions where the throttle valve is at or near its closed position. With the throttle valve being at or near its closed position, the flow through the induction passage is sonic and the induction passage air flow remains constant regardless of engine speed changes. Although the amount of fuel delivery to the engine changes in inverse proportion to the engine speed, the air flow actually introduced into the engine cylinder changes with a first order time lag relative to the engine speed change due to the influence of induction passage volume and cylinder stroke volume, shifting the air-fuel ratio from a desired value. The air-fuel ratio is enriched to an excessive extent causing unstable engine operation particularly when a great engine speed drop occurs with the throttle valve at or near its closed position.
Furthermore, the engine output torque increases with a first order time lag relative to the engine speed drop due to the time lag associated with the change of the engine cylinder air flow rate, causing engine stall particularly when a stepped drop occurs in engine speed during a transmission gear change.
Therefore, the present invention provides an improved engine control method and apparatus which can bring the actual torque produced at the engine output shaft quite close to the ideal torque required at the engine output shaft at the existing engine speed so as to permit transmission gear changes without engine stall.